1. Field of the Invention
This invention relates generally to snap rings designed for use in clean environments and particularly to snap rings for use in information storage devices.
2. Background Information
In hard disk drives, magnetic heads read and write data on the surfaces of co-rotating disks that are co-axially mounted on a spindle motor. The magnetically-written “bits” of written information are therefore laid out in concentric circular “tracks” on the surfaces of the disks. The disks must rotate quickly so that the computer user does not have to wait long for a desired bit of information on the disk surface to translate to a position under the head. In modern disk drives, data bits and tracks must be extremely narrow and closely spaced to achieve a high density of information per unit area of the disk surface.
The required small size and close spacing of information bits on the disk surface has consequences on the design of the disk drive device and its mechanical components. Among the most important consequences is that the magnetic transducer on the head must operate in extremely close proximity to the magnetic surface of the disk. However, because there is relative motion between the disk surface and the head due to the disk rotation and head actuation, continuous contact between the head and disk can lead to tribological failure of the interface. Such tribological failure, known colloquially as a “head crash,” can damage the disk and head, and usually causes data loss. Therefore, the magnetic head is typically designed to be hydrodynamically supported by an extremely thin air bearing so that its magnetic transducer can operate in close proximity to the disk while physical contacts between the head and the disk are minimized or avoided.
The head-disk spacing present during operation of modern hard disk drives is extremely small—measuring in the tens of nanometers. Obviously, for the head to operate so closely to the disk the head-disk interface must be kept clear of debris and contamination—even microscopic debris and contamination. In addition to tribological consequences, contamination and debris at or near the head disk interface can force the head away from the disk. The resulting temporary increases in head-disk spacing cause magnetic read/write errors. Accordingly, magnetic hard disk drives are assembled in clean-room conditions and the constituent parts are subjected to pre-assembly cleaning steps during manufacture.
Another consequence of the close spacing of information bits and tracks written on the disk surface is that the spindle rotation and head actuator motion must be of very high precision. The head actuator must have structural characteristics that allow it to be actively controlled to quickly seek different tracks of information and then precisely follow small disturbances in the rotational motion of the disk while following such tracks.
Characteristics of the actuator structure that are important include stiffness, mass, geometry, and boundary conditions. For example, one important boundary condition is the rigidity of the interface between the actuator arm and the actuator pivot bearing.
All structural characteristics of the actuator, including those mentioned above, must be considered by the designer to minimize vibration in response to rapid angular motions and other excitations. For example, the actuator arm can not be designed to be too massive because it must accelerate very quickly to reach information tracks containing desired information. Otherwise, the time to access desired information may be acceptable to the user.
On the other hand, the actuator arm must be stiff enough and the actuator pivot bearing must be of high enough quality so that the position of the head can be precisely controlled during operation. Also, the interface between the actuator arm and the pivot bearing must be of sufficient rigidity and strength to enable precise control of the head position during operation.
Actuator arm stiffness must also be sufficient to limit deflection that might cause contact with the disk during mechanical shock events that may occur during operation or non-operation. Likewise, the interface between the actuator arm and the pivot bearing must be of sufficient strength to prevent catastrophic structural failure such as axial slippage between the actuator arm and the actuator pivot bearing sleeve during large mechanical shock events.
In many disk drives, the actuator arm (or arms) is fixed to the actuator pivot bearing sleeve by a snap ring known as the actuator pivot bearing snap ring. The actuator pivot bearing snap ring typically includes one or more out-of-plane bends that function as a preloaded axial spring after assembly. The action of the actuator pivot bearing snap ring as a preloaded axial spring prevents separation and slippage at the interface between the actuator arm and the pivot bearing during operation and during mechanical shock events.
State of the art snap rings are typically metal parts that achieve their final shape through the use of a stamping die. The stamping die tends to slightly round the edges on one face of each snap ring. This rounding is known as stamping “die roll” and it can typically survive subsequent forming (e.g. coining) steps (if any).
The actuator pivot bearing snap ring may be installed with its face having edges with stamping die roll adjacent to and in contact with the actuator arm structure. In this case, the other face of the snap ring will be adjacent to and in contact with a surface of the pivot bearing sleeve. Alternatively, the actuator pivot bearing snap ring may be installed with its face having edges with stamping die roll adjacent to and in contact with the pivot bearing sleeve. In this case, the other face of the snap ring will be adjacent to and in contact with a surface of the actuator pivot bearing sleeve.
The actuator arm structure is typically fabricated from aluminum or an alloy of aluminum and is therefore typically softer and more easily burnished than the pivot bearing sleeve, which is typically fabricated from stainless steel. Therefore, less debris comprising aluminum are generated if a conventional snap ring is installed in an orientation such that its face having edges with stamping die roll are adjacent to and in contact with the actuator arm structure.
Although debris comprising aluminum may be reduced by specifying orientation of the snap ring when installed, most state-of-the-art attempts to improve post-fabrication cleanliness of disk drive components have focused on pre- and post-assembly cleaning steps and on environmental cleanliness during assembly. The industry's marked reliance on cleaning steps survives even though assembly in clean environments and post-assembly cleaning steps are not thorough in their removal of contaminants and debris. Less frequently, disk drive designers consider the generation of debris and contamination earlier in the design of sub-components. Still, such consideration is often restricted to the selection of lubricants and adhesives.
Consequently, there remains much scope in the art for reducing debris generation via novel changes to the basic design or assembly of various sub-components of the disk drive. Since only one of the faces of a conventional snap ring has stamping die roll, regardless of the snap ring's orientation one of its faces will be prone to generate debris (either through burnishing of the surface of the actuator arm structure or via contact with the pivot bearing sleeve).
Therefore, there is a need in the art for an actuator pivot bearing snap ring that can generally prevent or generally reduce the creation of debris during assembly rather than relying on debris removal by post-assembly cleaning steps. Although the need in the art was described above in the context of magnetic disk drive information storage devices, the need is also present in other applications where a snap ring is used in a clean environment that must remain as free as possible of debris and contaminants.